Optically transparent/colorless polyimides

Several series of linear aromatic polyimide films have been synthesized and characterized with the objective of obtaining maximum optical transparency. Two approaches have been used as part of this structure-property relationship study. The first approach is to vary the molecular structure so as to separate chromophoric centers and reduce electronic interactions between polymer chains to lower the intensity of color in the resulting polymer films. A second and concurrent approach is to perform polymerizations with highly purified monomers. Glass transition temperatures of thermally cured polyimide films are obtained by thermomechanical analysis and thermal decomposition temperatures are determined by thermogravimetric analysis. Transmittance UV-visible spectra of the polyimide films are compared to that of a commercial polyimide film. Fully imidized films are tested for solubility in common organic solvents. The more transparent films prepared in this study are evaluated for use on second-surface mirror thermal control coating systems. Lightly colored to colorless films are characterized by UV-visible spectroscopy before and after exposure to 300 equivalent solar hours UV irradiation and varying doses of 1 MeV electron irradiation. The effects of monomer purity, casting solvent and cure atmosphere on polyimide film transparency are also investigated

All crystal clear: 18th-century glass à la façon de Bohème from the cistercian nunnery of Clairefontaine, Belgium

Excavations at the Cistercian nunnery of Clairefontaine, located near Arlon in the south of Belgium, revealed an assemblage of 18th-century colorless glass. The morphology of the vessels and the engraved decoration suggest a central European origin or, at least, stylistic inspiration. The composition of the glass points to a recipe combining silica, lime, and potash: a colorless potash glass à la façon de Bohème. This article considers the technology, morphology, and origin of the vessels. The art-historical analysis is supported by chemical research (scanning electron microscopy–energy-dispersive X-ray spectroscopy [SEM-EDX]). The finds are also discussed in light of the emerging northwestern European glass industry, changing consumer practices during the 18th century, and their meaning for the inhabitants of the abbey

Silk oak flowers as a source of β-carotene

The pigment of the yellow flowers of the silk oak (Grevillea robusta, Cunningham) does not appear to have been investigated heretofore. If the dried material is extracted with ether, the solution shows typical absorption maxima at 483 and 453 mµ,corresponding to the spectrum of p-carotene. The rather blurred borders of these bands indicate, however, the presence of other polyenic pigments in small quantities. After saponification a photometric analysis of the total extract gave values which would correspond to 270 mg. of β-carotene in 1 kilo of the dry flowers if no other pigments were present. After a chromatographic separation the true β-carotene content was found to be about 215 mg. per kilo. Two-thirds of this amount was isolated as crystals; lycopene or γ- and α-carotene were not present [1]. The non-carotene fraction is a complicated xanthophyll mixture in which no single compound predominates. From this fraction two very small amounts of crystalline material were isolated, one of which was kryptoxanthin and the other a new carotenoid possessing a remarkably short wave-length spectrum. For the separation and study of carotenoids contained in extracts we suggest the systematic use of the ultraviolet lamp which has been so helpful in the chromatography of colorless substances (2). Plant pigments are frequently accompanied by large amounts of colorless material which prevent the formation of sharp pigment zones in the Tswett column and thus a satisfactory separation of the components. Furthermore, the crystallization of some carotenoids may be hindered. Fortunately many such colorless substances show an intense fluorescence (3). An observation made in ultraviolet light during the chromatographic separation of the pigments may furnish a good indication of the best method and optimum extent of developing the chromatogram. The distribution of the fluorescence may also indicate the lines at which it is best to cut the column. By sacrificing small amounts of pigment large portions of colorless associated material may be eliminated in this simple way

Colorless operators in a non-associative quantum theory

The associators/antiassociators for the product of four non-associative operators are deduced. By analogy with SU(3) gauge theory the notion of colorless (white) operators is introduced. Some properties of white operators are considered. It is hypothesized that white operators do not give any contribution to corresponding associators/antiassociators. It is suggested that the observables in a non-associative quantum theory correspond to the white operators only.Comment: final version, title and text are change

Xenon forms stable compound with fluorine

Experiments show that xenon and fluorine combine readily at 400 deg C to form xenon tetrafluoride, which is colorless, crystalline, chemically stable and solid at room temperature. This process can be used for the separation of xenon from mixtures with other noble gases

The Boltzmann equation for colourless plasmons in hot QCD plasma. Semiclassical approximation

Within the framework of the semiclassical approximation, we derive the Boltzmann equation describing the dynamics of colorless plasmons in a hot QCD plasma. The probability of the plasmon-plasmon scattering at the leading order in the coupling constant is obtained. This probability is gauge-independent at least in the class of the covariant and temporal gauges. It is noted that the structure of the scattering kernel possesses important qualitative difference from the corresponding one in the Abelian plasma, in spite of the fact that we focused our study on the colorless soft excitations. It is shown that four-plasmon decay is suppressed by the power of $g$ relative to the process of nonlinear scattering of plasmons by thermal particles at the soft momentum scale. It is stated that the former process becomes important in going to the ultrasoft region of the momentum scale.Comment: 41, LaTeX, minor changes, identical to published versio

Screen of cylindrical lenses produces stereoscopic television pictures

Stereoscopic television pictures are produced by placing a colorless, transparent screen of adjacent parallel cylindrical lenses before a raster from two synchronized TV cameras. Alternate frames from alternate cameras are displayed. The viewers sensory perception fuses the two images into one three-dimensional picture